ZURICH, Sept 25 (Reuters) - A drug cocktail with Roche’s Tecentriq added two months to small-cell lung cancer patients’ lives, potentially aiding the Swiss company’s bid to win approval in a niche disease area before rivals that now dominate the immunotherapy market.

Patients with untreated extensive-stage small-cell lung cancer (SCLC), where cancer has spread beyond the lungs, lived a median 12.3 months after getting Tecentriq plus chemotherapy, data released on Tuesday at the International Association for the Study of Lung Cancer’s annual conference in Toronto showed.

That compared to 10.3 months for those receiving a chemotherapy regimen of carboplatin plus etoposide.

Roche had said in June that its IMpower 133 trial was positive, but had not given the scale of the benefit.

Tecentriq has trailed Merck’s Keytruda and Bristol Myers Squib’s Opdivo in revenue as its rivals’ medicines beat it to market in other indications. Merck’s drug has also posted more-convincing trial results in lucrative non-small-cell lung cancer (NSCLC), which hits some 85 percent of patients.

“The addition of (Tecentriq) to chemotherapy in the first-line treatment of extensive-stage small-cell lung cancer resulted in significantly longer overall survival,” doctors who conducted the 403-patient IMpower 133 study wrote in the New England Journal of Medicine in an abstract published on Tuesday.

Baader Helvea analysts have said a potential “first-mover advantage” in small cell lung cancer could add $1.5 billion to Tecentriq’s peak sales.

ALSO-RAN

In addition to keeping a lid on costs, Schwan has pegged Tecentriq as a pivotal piece in plans to counterbalance $21 billion in revenue at risk with patent expirations on the Basel-based drugmaker’s three top sellers, Rituxan, Herceptin and Avastin.

So far, however, Roche’s medicine, which like the Bristol and Merck drugs works by helping take the brakes off the immune system, has largely played the part of commercial also-ran.

Earlier this month, U.S. regulators extended their review of the immunotherapy for first-line NSCLC by three months, a further hit to sales that trail rival products.

In the first half of 2018, Tecentriq chalked up 320 million Swiss francs ($333.7 million), while Keytruda and Opdivo sales were nearly 10-fold higher, with each at around $3.1 billion. ($1 = 0.9590 Swiss francs) (Reporting by John Miller; Editing by Michael Shields)